The optical accessing system has been widely used for data reading and data recording in present. However, because of the material characteristics of the storage medium within the optical accessing system and the accuracy of accessing method applied in the optical accessing system, the capacity of data can be recorded in an optical disc by a conventional optical disc accessing technology is limited. Therefore, an optical holography technology (or holographic data storage technology) is developed for raising the recording density on an optical disc.
FIG. 1 depicts a diagram of a holographic optical accessing system 100, wherein the holographic optical accessing system 100 includes: a signal beam 12, a data plane 14, a reference beam 16, a storage medium 18, a data beam 22, and a detecting apparatus 20.
When the data recording is processed in the holographic optical accessing system 100, a light beam, e.g. a laser beam emitted from a laser, is split into two light beams by a beam splitter (not shown), wherein one of the two light beams is regarded as the signal beam 12 after the light beam is emitted to the data plane 14, because the image information presented on the data plane 14 is also contained in the signal beam 12; another light beam split from the laser beam is regarded as the reference beam 16.
During the process of data recording, the signal beam 12 and the reference beam 16 are both focused on a focus point 24 of the storage medium 18 at the same time, wherein the storage medium 18 can be a photosensitive interface, such as photopolymer. When the signal beam 12 and the reference beam 16 are both focused on the focal point at the same time, the interference stripes are formed on the focus point 24, so as the image information which is contained in the signal beam 12 is recorded on the focal point 24 as a grating, and the data recording process is completed.
During the process of data reading in the holographic optical accessing system 100, only the reference beam 16 is focused on the focus point 24. After the reference beam 16 is focused on the focal point 24, a data beam 22 is then generated and propagates through the rail of the signal beam 12. The data, recorded on the focal point 24, is read out, so as the image information originally stored on the data plane 14 is also contained in the data beam 22. When the data beam 22 is received by the detecting apparatus 20 placed on the path of the data beam 22, the image information originally written on the data plane 14 will be projected on the detecting apparatus 20 and the data reading process is completed.
In addition, the data plane 14 is a SLM (Spatial Light Modulator), and the SLM can be a DMD (Digital Micro-mirror Device), a LCD (Liquid Crystal Display), or a LCOS (Liquid Crystal on Silicon), wherein the DMD, LCD, or LCOS are all composed by a plurality of displaying units arranged as an array, and image information can be presented by these displaying units with light states or dark states. The detecting apparatus 20 can be a CMOS (Complementary Metal-Oxide Semiconductor) or a CCD (Charge Coupled Device).
In the holographic optical accessing system 100, data is recorded in the storage medium 18 via the signal beam 12 and the reference beam 16 focused on the focal point 24 at the same time, wherein the signal beam 12 and the reference beam 16 are on-axis with each other. FIG. 2 illustrates the signal beam 12 and the reference beam 16 processing a data recording in the conventional holographic optical accessing system 100, wherein the signal beam 12 and the reference beam 16 have the same optical axis 15 and is so called on-axis. That means both the signal beam 12 and the reference beam 16 are contained in a light beam. As depicted in FIG. 2, when the signal beam 12 and the reference beam 16 are focused on the focal point 24 of the storage medium 18 at the same time via the lens module 19, the interference stripes are formed on the focal point 24, so as the data recording process is completed. However, because the signal beam 12 and the reference beam 16 are both further reflected back from the storage medium 18 to the lens module 19 via the same optical path, a crosstalk interference could be introduced by a conjugate light of the signal beam 12 and the conjugate light of the reference beam 16, so as the data recording accuracy is affected. Therefore, providing a holographic optical accessing system for fixing the above-described problem is the purpose of the present invention.